equilibrium amounts?

[aronno]

example;

Fe³⁺ + SCN^-  <---> Fe(SCN)²⁺

If we added Fe³⁺ to system. Therefore equilibrium is distrubed.
what is the final amount if the ion Fe³⁺. Greater less than or equal to.

I have come across these questions is text books. And from my understanding to see if the amount has incresed or... etc.
We look at wether the curve line goes up or down. (i.e like temp changes that produce the curved line in the graph.)
So if the curve goes up then the amount inreases.


My answer; I would say its less than before.

Am i doing this right???

[TrueTears]

Assuming initially the system is at equilibrium.

Adding more will favour the forward reaction.

There will be a sudden increase in the concentration of on a conc-time graph then it will slowly drop (but not to it's initial value because it only partially opposes this change).

Hence the final concentration (and mol) of is greater than before.

[aronno]

So we look at the overall change in concentration via graphs and if the line representing Fe3+ is higher than previous equilibrium. The OVERALL CONC. and AMOUNT INC.
right?

[TrueTears]

What you mean overall?

Just draw your normal conc-time graph... heaps of examples in heinemann if you are using it.

[aronno]

ya know how there is a sharp change in the conc. of Fe3+ and a gradual decrease. BUT "the line never goes below previous equilibrium" this tells us the concentration is greater than prvious equilibrium state.

right?

so the higher overall concentration = a higher overall amount(mol) of Fe3+, that is greater than previous equilibrium.

[TrueTears]

Eh I don't get your meaning of overall but anyways, yes there is a sharp increase in the conc of (a vertical line going straight up). Then it decreases gradually to a horizontal line but this horizontal line is higher than the original horizontal line of in the previous equilibrium. Hence concentration of increases.

[aronno]

OK so if the concentration overall has increased does that mean the amount overall has icreased?

[TrueTears]

OK so if the concentration overall has increased does that mean the amount overall has icreased?

Yeah I guess so. But always safer to just do a quick sketch of the conc-time graph, makes it much easier and safer.

[aronno]

hold on so if we added water to the system, everything decreases in concentration graph initially. however (in terms of Fe3+) the gradual/consequesnt change in concentration (i.e the curved line after the sharp vertical down!)
trys to increase concnetraion but, the overall concentration is lower than before. So does this mean the (amount/)Mole is lower than before.

the graph; (dilution)


 --------         
           l     .  .   .  .  . .  .  .  .  .  .  . (Fe3+ concentration) 
           l  .
           l.
(dots repressent the consequent change)
HENCE OVERALL CONC. IS LOWER and the OVERALL AMOUNT IS LOWER.

[TrueTears]

True.

But you said you added not water.

[aronno]

but in terms of dilution forgetting about adding the Fe3+. Is my reasoning correct?
DILUTION ONLY.

[TrueTears]

True.

[Mao]

Be careful with the use of 'overall amount'. In case of dilution, the overall concentration decrease, and consequently the equilibrium position shifts to the side with more particles. When equilibrium re-establishes, the concentrations (M, molar, as in mol/litre) of each species will still be lower than initial, but the amount (usually referring to total number of moles) of Fe³⁺ will have increased (and consequently, total mass of Fe³⁺ in the solution).

[Gloamglozer]

Be careful with the use of 'overall amount'. In case of dilution, the overall concentration decrease, and consequently the equilibrium position shifts to the side with more particles. When equilibrium re-establishes, the concentrations (M, molar, as in mol/litre) of each species will still be lower than initial, but the amount (usually referring to total number of moles) of Fe³⁺ will have increased (and consequently, total mass of Fe³⁺ in the solution).

Ah yes, I remember my teacher telling me this today and how this doesn't follow "normal logic" because if you increase the amount of something, usually you increase its concentration as well but in this case, it's the opposite.

[TrueTears]

Be careful with the use of 'overall amount'. In case of dilution, the overall concentration decrease, and consequently the equilibrium position shifts to the side with more particles. When equilibrium re-establishes, the concentrations (M, molar, as in mol/litre) of each species will still be lower than initial, but the amount (usually referring to total number of moles) of Fe³⁺ will have increased (and consequently, total mass of Fe³⁺ in the solution).

Ah yes, I remember my teacher telling me this today and how this doesn't follow "normal logic" because if you increase the amount of something, usually you increase its concentration as well but in this case, it's the opposite.

Exactly, that is why I did not get aronno's meaning of "overall", it is too ambiguous.